RFPIC12C509AG Microchip Technology Inc., RFPIC12C509AG Datasheet - Page 32

• Manufacturer Part Number: RFPIC12C509AG
• Description: 18/20-pin 8-bit Cmos Microcontroller With Uhf Ask/fsk Transmitter
• Manufacturer: Microchip Technology Inc.

rfPIC12C509AG/509AF
6.2
An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer (WDT), respectively (Section 8.6). For simplicity,
this counter is being referred to as “prescaler” through-
out this data sheet. Note that the prescaler may be
used by either the Timer0 module or the WDT, but not
both. Thus, a prescaler assignment for the Timer0
module means that there is no prescaler for the WDT,
and vice-versa.
The PSA and PS2:PS0 bits (OPTION<3:0>) determine
prescaler assignment and prescale ratio.
When assigned to the Timer0 module, all instructions
writing
MOVWF 1, BSF 1,x, etc.) will clear the prescaler.
When assigned to WDT, a CLRWDT instruction will clear
the prescaler along with the WDT. The prescaler is nei-
ther readable nor writable. On a RESET, the prescaler
contains all '0's.
6.2.1
The prescaler assignment is fully under software con-
trol (i.e., it can be changed “on the fly” during program
execution). To avoid an unintended device RESET, the
following instruction sequence (Example 6-1) must be
executed when changing the prescaler assignment
from Timer0 to the WDT.
DS70031A-page 30
to
Prescaler
SWITCHING PRESCALER
ASSIGNMENT
the
TMR0
register
(e.g.,
CLRF 1,
Preliminary
EXAMPLE 6-1:
To change prescaler from the WDT to the Timer0 mod-
ule, use the sequence shown in Example 6-2. This
sequence must be used even if the WDT is disabled. A
CLRWDT instruction should be executed before switch-
ing the prescaler.
EXAMPLE 6-2:
CLRWDT
MOVLW
OPTION
1.CLRWDT
2.CLRF
3.MOVLW
4.OPTION
5.CLRWDT
6.MOVLW
7.OPTION
'xxxx0xxx'
TMR0
'00xx1111’b ;These 3 lines (5, 6, 7)
'00xx1xxx’b ;Set Postscaler to
Changing Prescaler
(Timer0 WDT)
Changing Prescaler
(WDT Timer0)
©
2001 Microchip Technology Inc.
;Clear WDT
;Clear TMR0 & Prescaler
; desired
;PS<2:0> are 000 or 001
; are required only if
; desired WDT rate
;Clear WDT and
;prescaler
;Select TMR0, new
;prescale value and
;clock source